The present invention concerns the alignment of an optical fiber to a light source or to a light detector before permanent attachment.
When attaching an optical fiber to a light source, for example a laser diode or a light emitting diode (LED), or to a light detector, for example a PIN detector, alignment is critical. Alignment is a complicated process due to the fact that the narrow diameter of an optical fiber and the limited size of a chip which serves as a light source or light detector. For example, the diameter of an optical fiber is typically 62.5 micrometers. A PIN detector typically has an active area with a diameter of approximately 60 micrometers. An LED typically has a light emission area with a diameter of 20 micrometers. Therefore, accuracy of alignment within a micrometer is essential. A misalignment by even a couple of micrometers can cause a variation in optical power budget loss of a few dBm.
Until recently, alignment was generally performed manually. Highly experienced operators would use manual positioning stages, optical power meters and large doses of patience to align an optical fiber for attachment to a light source or a light detector. More recently automated systems have been used for such alignment. A typical automated alignment system usually includes mechanical, electrical and electro-optical components and instrumentations controlled by a computer system.
In a typical automated alignment system either a light source (e.g. LED) or a light detector (e.g. PIN detector) is assembled on a circular header. The resultant assembly is then tested. After testing, the assembly is aligned to the fiber optical connector receptacle. Once aligned, the fiber optical connector receptacle is permanently attached and sealed to the assembly in the aligned position to form an optical subassembly (OSA).
Typically, alignment of the assembly of the fiber optical receptacle is done as follows. A fiber ferrule is plugged into the connector receptacle to monitor resultant light power from a light source or to measure resultant current from a light detector. A header portion of the optical fiber is then moved in an X-Y plane parallel to the plane in which the emission area or the detection area resides. The header portion is left at the X-Y coordinates which result in the maximum output power. The port cap or connector receptacle is then moved along a Z-axis perpendicular to the plane in which the emission area or detection area resides. This is done to focus the light beam in order to find the location along the Z-axis where maximum output power is reached. Then the header is again varied in the X-Y plane to find the position of maximum power. At this point, the OSA is ready for permanent attachment.